1. Field of the Invention
The present invention relates to an apparatus for limiting the transfer of force to surgical instruments.
The invention further concerns surgical instruments which are equipped with an apparatus of this kind.
Surgical instruments of this kind may be grasping, holding, and dissection forceps, scissors, or other instruments in which working part, usually mouth parts, are moved by manual force via an actuation element that can be moved back and forth.
2. Related Prior Art
Grasping, holding, and dissection forceps are known, for example, from the catalog "Endoskopische Chirurgie [Endoscopic surgery], 2nd edition, 1/94, section 4, Praparier- und Fa.beta.zangen [Dissection and grasping forceps]" of Karl Storz GmbH & Co., Tuttlingen, Germany.
These known forceps have an elongated cylindrical shaft at whose distal end at least two mouth parts are arranged. Arranged at the proximal end of the shaft is a handle which has the form of two scissor-like handle elements. One of the handle elements is immovably joined to the shaft, and the other, called the movable handle element, is joined via a hinge to the immovable handle element. A mechanism which serves to open and close the mouth parts has a rod-shaped actuation element, passing through the shaft, which is joined at the distal end to the mouth parts. At the proximal end, the actuation element extends out beyond the end of the stationary handle element and is joined in articulated fashion, usually via a ball-and-socket joint, to the upper outer end of the movable handle element. Pivoting of the movable handle element about the hinge axis relative to the stationary handle element causes a linear back-and-forth displacement of the actuation element in the shaft. This linear or axial back-and-forth movement is converted into a pivoting movement of the mouth parts.
Forceps of this kind are utilized in the commonly-used practice of minimally invasive surgery. In this context, the forceps are introduced into the body through trocars.
Because of the miniaturization of the mouth parts necessary for minimally invasive surgery, they are sensitive to loads, since for given hand forces the sustainable forces become smaller due to miniaturization. This also applies to dynamic devices of normal size if the design load is exceeded. The movable handle element is configured as a lever, the lever axis being represented by the hinge axis at which the movable handle element is articulated onto the other handle element. The distance from the hinge axis to the point at which the movable handle element is connected to the actuation element that is to be displaced is much shorter than the distance from the hinge axis to the finger loop arranged at the outer end of the handle element. The ratio is approximately 10:1, i.e. the closing force of a hand, approximately 10 kp, is amplified tenfold by the lever effect, i.e. to approximately 100 kp. A limitation of force is not present with the embodied kinematics of the known forceps.
In the practical utilization of surgical grasping and holding forceps, is has been found that during handling an attempt is made to clamp the object being held, for example a spherical sponge or a needle, as firmly as possible in the grasping forceps. In the case of cutting and in particular cut-through mouth parts there may be a risk, if instead of an easily cut soft tissue element a piece of cartilage or bone ends up between the mouth points, that the operator will exert a closing force which exceeds the force that can be safely sustained by the mouth parts. Strong persons can exert a closing force of 15 kp or more, which is then amplified tenfold by the lever. If overloading due to the exertion of excessive hand force, and thus high loading of the mouth parts, occurs frequently, this can cause material fatigue in the mouth part region and even breakage of the mouth parts. There exists in this context the risk that the aforesaid breakage of the mouth parts due to overloading might occur during the operation. This can result in uncontrolled damage to tissue and organs in the operative area.
DE 38 19 123 A1 discloses a surgical instrument that is equipped with an overload protector. The overload protector comprises a force reservoir which absorbs the increased tension. In the simplest case, the force reservoir comprises a helical spring.
DE 41 31 176 A1 discloses a medical instrument in which, in an overload situation, spreading of an element of the actuation rod results in positive engagement into a stationary portion of the forceps housing, e.g. by way of an elastic tubular piece.
DE 94 07 081 U1 discloses an overload protection system for motor-driven surgical instruments which can be configured as a claw coupling, friction coupling, magnetic coupling, or defined break point.
Against this background, it is the object of the present invention to create an apparatus with which overloads on the working parts of a surgical instrument can be reliably prevented.